DLG4 and amyotrophic lateral sclerosis: Considering synaptic dysfunction, data demonstrated that mSOD1 MNs have increased presynaptic synaptophysin and decreased postsynaptic density protein 95 (PSD-95) gene expression levels (Figure 3e,f; at least p < 0.01 vs. untreated WT MNs), confirming trans-synaptic signaling impairment in ALS MNs.